Refractory wound is a major clinical problem in diabetic patients that often leads to amputations. Recent studies including ours suggest that endothelial progenitor cells (EPCs), precursor of mature endothelial cells, critically contribute to local angiogenesis in wound repair, providing th proof of concept of EPC-based cell therapy for diabetic wounds. However, EPC angiogenic functions are severely impaired in both type 1 and type 2 diabetic patients, directly limiting thei potential for autologous cell therapies clinically. MicroRNAs are a new class of small endogenous non-coding RNAs that may exert their therapeutic potential as key post-transcriptional regulators. Among all miRNAs, less than 10 of them have been reported to exert pro- or anti-angiogenic effects in mature endothelial cells to date. Remarkably, little information exist on miRNA regulation of EPC-mediated angiogenesis, especially under disease conditions. This competitive renewal proposal focuses on pro-angiogenic microRNA mir-27b because our preliminary studies indicate that it is deficient in diabetic EPCs, and its restoration rescues EPC functions and accelerates diabetic wound healing. The mechanisms underlying this fascinating phenomenon remain unclear. We hypothesize that mir-27b directly suppresses a novel pro-oxidant ShcA protein p66shc and/or potent anti-angiogenic protein thrombospondin-2 (TSP-2), with increased manganese superoxide dismutase (MnSOD) and reduced mitochondrial oxidative stress that result in improved EPC angiogenic function and accelerated wound healing in type 2 diabetes. This hypothesis is formulated after a careful analysis of published work in the field and the generation of some key preliminary data in our laboratory during the last funding period. We plan to test our central hypothesis and accomplish our objective by pursuing three specific aims. In Aim 1, we will determine how mir-27b improves EPC angiogenic function in diabetes. In Aim 2, we will determine the direct target of mir-27b in diabetic EPCs. In Aim 3, we will examine the functional consequences of mir-27b targeted EPC cell therapy on wound healing in diabetes. The major significance of this study is that it will delineate for the first tme how miRNAs regulate EPC angiogenesis and wound repair in diabetes. Determine how diabetic EPC functions are regulated by pro-angiogenic mir-27b could lead to improved autologous EPC cell therapy with miRNA modification for refractory wounds in increasing number of diabetic patients who suffer from this devastating complication.